New electron temperature diagnostic of critical surface based on the ion acoustic decay instability in hot, high density plasma relevant to laser fusion. Semiannual report, April 1--September 29, 1994

摘要

The authors made analysis of the IADI experiments previously made using OMEGA laser system. They obtained two important new results: the first direct observation of the epw excited by the Ion Acoustic Decay Instability, and the first study of the IADI in a plasma that approaches laser-fusion conditions, in the sense of having a density scale length of order 1 mm and an electron temperature, T(sub e), in excess of 1 keV. Previous observations of the epw's have been based on the second harmonic emission, from which little can be inferred because the emission is produced by unknown pairs of epw's, integrated in a complicated way over wavenumber space and real space. In contrast, they have directly observed the epw by using the 90(degree), collective Thomson scattering (CTS) of a UV laser (at the third harmonic of the pump) from the epw's. Because the ratio of probe frequency to electron plasma frequency is only about three, the scattering is collective (i.e. k(sub epw)(lambda)(sub De) is small, where k(sub epw) is the epw wave number and (lambda)(sub De) is the Debye length),m even though the scattering angle is large. The electron temperature can then be deduced from the ion sound velocity, obtained from the measurement of the frequency at which growth is maximum at the scattering wavenumber.